UFO=飞碟

UFO现象的产生,给地球人类带来了一个奇妙的话题和无限的遐想:UFO是什么?UFO现象对人类产生了哪些影响?在广漠浩瀚的宇宙中是否有高级生命形式存在?等等。对困扰了人们几十年的UFO现象,广大青少年朋友也很感兴趣,同时也产生了一些困惑。为了科学地解释UFO现象,我刊与中国UFO研究会合作,从本期起,开辟了这个“UFO之谜”栏目,邀请有关专家和人员来谈谈UFO这个话题。青少年朋友看过这个栏目后,有什么想法和疑问欢迎来信,我们将在“UFO信箱”中予以解答并和青少年朋友共同探讨感兴趣的话题。     

非线性微分方程y′=sum from i=0 to n (a_i(x)y~i)解空间的显易结构

文章给出了非线性微分方程,具有“第一显易结构”的充分必要条件。     

美国IBM公司i系列首席科学家Frank Soltis访问我校

5月2 8日下午,我校校长李未院士在如心会议中心亲切会见了来访的美国IBMi系列的首席科学家FrankSoltis博士发明了当今IBMe’serveri系列服务器中最具创新性的计算机体系结构,由他首次提出的独立于技术的机器接口和单层寻址功能促使了一种全新品种计算机的产生。FrankSoltis博士     

Heusler合金M2CoA(M=Mn,Ti;A=Al,Si)的第一性原理

采用基于密度泛函理论(DFT)的第一性原理计算方法,研究了M₂CoA型Heusler合金Mn₂CoAl、Mn₂CoSi、Ti₂CoAl和Ti₂CoSi的电子结构和磁学性质。发现Heusler合金Mn₂CoAl是亚铁磁性自旋无带隙半导体,Mn₂CoSi与Ti₂CoAl是亚铁磁性自旋半金属,而Ti₂CoSi是铁磁性自旋半金属。它们的总自旋磁矩均为整数,符合Slater-Pauling规则。然后,在分析电子能带结构和态密度的基础上,探讨了自旋无带隙半导体与半金属性的根源。最后,声子谱和弹性常数计算结果表明所有M₂CoA型Heusler合金在晶格动力学和力学上均是稳定的。     

不定方程x~4+y~4+z~4=ω~2的解

本文论证了不定方程x~4+y~4+z~4=ω~2存在正整数解,并给出了解的表达式,从而为讨论不定方程x~4+y~4+z~4=ω~4是否存在正整数解奠下了基石。     

关于双曲型偏微分方程u_xy=f(X,y,u)的唯一性

本文给出双曲型偏微分方程的特征边值问题 u_xy=f(x,y,u), u(x,O)=σ(x), O≤x≤a, u(O,y)=T(y), O≤y≤b, 在R=[O,a]×[O,b]上的解u=u(x,y)的唯一性定理。     

X_2H_6（X=ⅢA族）化学键的量子化学研究（英文）

在CCSD/6-311＋＋G（3df,3pd）的计算水平对X2H6（X=ⅢA族）的结合能和化学键进行了理论研究.结果表明,X2H6都具有与B2H6相似的几何结构,分子中存在两个共平面的三中心两电子氢桥键τM—H＇—M.考虑了XH3单体结合成二聚体时的变形能和基组重叠误差（BSSE）,B2H6,Al2H6,Ga2H6,In2H6和Tl2H6的结合能分别为167.7,150.6,106.5,97.4和79.3kJ/mol.桥氢原子（H＇）具有比σ-氢原子（H）更负的原子极化张量电荷.X—H的键级为0.961.00,以共价性为主.而X—H的键级为0.400.47,以离子性为主（B2H6除外）.在B2H6,Al2H6,Ga2H6,In2H6和Tl2H6中,X—H共价性百分比分别是96.3%,62.3%,70.2%,59.0%和68.6%,而X—H离子性百分比分别是47.9%,68.1%,62.9%,71.5%和69.4%.B2H6的主要共振结构是H＋[B2H5]-（占37.22%）,而其他二聚体的主要共振结构是XH3.XH3（占61.77%-69.75%）.     

非晶态Co-T-Zr(T=Cr,Mo,V,W)合金作为磁强计磁芯材料的研究

以快淬法制备了非晶态Co_(90～x)T_xZr_(10)(T=Cr,Mo,V,W;x=0,4,6,8,10,12)合金系列样品,并对其一些热和磁性能进行了测试研究,探讨了它们在磁强计上应用的可能性。结果表明,随着样品中T元素含量的增加,样品的晶化温度和晶化激活能升高,饱和磁化强度和居里温度下降,交流磁导率变化不大。退火处理对交流磁导率和损耗有较大影响。以现有理论对实验结果进行了分析。非晶态Co_(78)Cr_(12)Zr_(10)合金适于用作磁强计探头的磁芯材料,尤其是它良好的高频性能使磁强计测量的交流磁场的截止频率大干20kHz。     

Kink mode m = 1 in magnetic tube with discontinuous magnetic field

In this paper, we study conditions of realization and stability of kink modes with azimuthal wave numbers $m=\pm 1$ in cylindrical plasma flex with twisted magnetic field and homogeneous current along its axis. We assume permanent axial magnetic field both inside and outside the flex, surrounded by currentless plasma. Azimuthal magnetic field decreases inversely proportional to the distance from the boundary beyond the flex. We derived dispersion equations for stable and unstable modes in approximation of “thin” plasma flex. The analysis of equations has been provided for the case of discontinuous axial magnetic field on flex’s boundary. Conditions of propagation of wave modes have been defined. It was shown, that unstable modes can be implemented in certain interval of longitudinal wavenumbers. Results can be applied for the interpretation of solar magnetic tubes behavior, using measurements, provided by spacecrafts.     

Rare observation of daytime whistlers at very low latitude (L = 1.08)

The source region and propagation mechanism of low latitude whistlers (Geomag. lat. <30°) have puzzled scientific community for last many decades. In view of recent reports, there is consensus on the source region of low latitude whistlers in the vicinity of the conjugate point. But the plausible conditions of ionospheric medium through which they travel are still uncertain. In addition to that, the whistlers in daytime are never observed at geomagnetic latitudes less than 20°. Here, for the first time, we present a rare observations of whistlers during sunlit hours from a very low-latitude station Allahabad (Geomag. Lat: 16.79°N, L = 1.08) in India on 04 February 2011. More than 90 whistlers are recorded during 1200–1300 UT during which the whole propagation path from lightning source region to whistler observation site is under sunlit. The favorable factors that facilitated the whistlers prior to the sunset are investigated in terms of source lightning characteristics, geomagnetic and background ionospheric medium conditions. The whistler activity period was found to be geomagnetically quiet. However, a significant suppression in ionospheric total electron content (TEC) compared to its quiet day average is found. This shows that background ionospheric conditions may play a key role in low latitude whistler propagation. This study reveals that whistlers can occur under sunlit hours at latitudes as low as L = 1.08 when the source lightning and ionospheric medium characteristics are optimally favorable.